Edge Heat Research Articles

Heat Pipe Thermal Management at Hypersonic Vehicle Leading Edges: A Low-Temperature Model Study

The intense thermal fluxes and aero-thermomechanical loads generated at sharp leading edges of atmospheric hypersonic vehicles traveling above Mach 5 have motivated an interest in novel thermal management strategies. Here, we use a low-temperature stainless steel-water system to experimentally investigate the feasibility of metallic leading edge heat pipe concepts for thermal management in an efficient load supporting structure. The concept is based upon a two-phase, high thermal conductance “heat pipe” which redistributes the localized thermal flux created at the leading edge stagnation point over a larger surface for effective removal. Structural efficiency is achieved by configuring the system as a wedge-shaped sandwich panel with an I-cell core that simultaneously permits axial vapor and returns liquid flow. The measured axial temperature profiles resulting from a localized thermal flux applied to the tip are consistent with effective thermal spreading that lowered the peak leading edge temperature and reduced the temperature gradients when compared with an equivalent structure containing no working fluid. A simple finite element model that treated the vapor as an equivalent, high thermal conductivity material was in good agreement with these experiments. The model is then used to design a niobium alloy-lithium system that is shown to be suitable for enthalpy conditions representative of Mach 7 scramjet-powered flight. The study indicates that the surface temperature reductions of heat pipe-based leading edges may be sufficient to permit the use of nonablative, refractory metal leading edges with oxidation protection in hypersonic environments.

Study of heating characteristics for a continuous 915 MHz pilot scale microwave thawing system

Heating uniformity is the critical control point on quality and safety during microwave thawing process. The objective of this study was to investigate heating characteristics of a continuous 915 MHz pilot scale microwave thawing system with a numerical simulation model and experiments. The microwave frequency and physical properties of frozen surimi were measured to provide essential information for the numerical simulation model. To validate the developed model, infrared camera and fiber optic sensors were utilized to capture the heating pattern and record the time-temperature profiles of the processed surimi. Volume percentages of the obtained temperature data for both simulated and experimental results were calculated and plotted into curves to intuitively show the heating characteristics. Results showed that the operating frequency of the thawing system was changing with time and affected by presence of load. Simulation results showed that the overall heating pattern was not sensitive to frequency settings. However, different frequency settings brought big difference of local temperature which implied varying microwave energy concentration at different frequencies. Experimental results showed good repeatability and agreed well to simulation results in heating pattern but not in temperature profiles due to varying frequencies. Simulation models with combined frequencies were recommended to improve temperature accuracy. Sample distance and size for continuously moving surimi slabs were studied using developed simulation model. It illustrated that smaller sample distance reduced the edge heating in moving direction. And a larger size of food in moving direction brought better heating uniformity.

Thermal Simulations of High Current β-Ga2O3 Schottky Rectifiers

The temperature rise and distribution in large area β-Ga2O3 rectifiers is simulated using self-consistent solution of the partial differential equations governing the physics in the electrical and thermal domains with the Florida Object Oriented Device and Process simulator (FLOODS) TCAD simulator. The effect of forward voltage (0−2.5V) and power (0−5.5W) was examined for the different epitaxial layer and bulk substrate thicknesses, as well as edge termination and heat sink geometry. A higher maximum temperature is seen for the devices with thicker bulk substrates, while the effect of Joule heating was more evident in the thinner epi-layer structures since the resistance decreases and the power generation increases, resulting in a higher temperature. The maximum temperature rise was ∼170K under high power conditions. The heat sink simulation results show a drop in the maximum temperature, where a Cu fin heat sink reduced the maximum temperature by 26.76%.

Measuring heat flux to a porous burner in microgravity

Flame heat flux absorbed by a porous gas-fueled burner is measured in microgravity. The burner's perforated copper plate serves as a slug calorimeter in which two heat flux thermopile sensors are embedded. The slug calorimeter provides the average heat flux over the burner surface as a function of time. The 25 mm diameter burner is calibrated as a slug calorimeter in normal gravity using a known radiative heat flux with step changes. Microgravity diffusion flames were observed in NASA Glenn's 5.18-s Zero Gravity Research Facility, and average heat fluxes measured with the calorimeter agree with the locally measured heat fluxes through a theoretical distribution function. The results show that the average slug calorimeter heat flux and the two local heat flux measurements are in harmony over a wide range of microgravity flame fluxes ranging from 5–20 kW/m2, with the edge heat flux much higher. Transient and nearly steady results are presented.

Transient analysis of a circular foil gage in a convective and radiative environment

An analysis of a circular thin-foil gage is presented that includes transient effects, convective heat transfer, and an arbitrary time-varying boundary condition at the foil edge to account for fluctuations in cooling water temperature. The governing energy equation is solved using Laplace transform to obtain the temporal and spatial temperature distributions of the foil. Under constant temperature at the foil edge and constant thermal radiative heat flux, closed-form response curves for the gage under various modes of heat transfer are provided. Steady-state results are also presented as limiting cases.

Magnetic configuration effects on the edge heat flux in the limiter plasma on W7-X measured using the infrared camera and the combined probe

Controlling the heat and particle fluxes in the plasma edge and on the plasma facing components is important for the safe and effective operation of every magnetically confined fusion device. This was attempted on Wendelstein 7-X in the first operational campaign, with the modification of the magnetic configuration by use of the trim coils and tuning the field coil currents, commonly named iota scan. Ideally, the heat loads on the five limiters are equal. However, they differ between each limiter and are non-uniform, due to the (relatively small) error fields caused by the misalignment of components. It is therefore necessary to study the influence of the configuration changes on the transport of heat and particles in the plasma edge caused by the application of error fields and the change of the magnetic configuration. In this paper the up-stream measurements conducted with the combined probe are compared to the downstream measurements with the DIAS infrared camera on the limiter.

Turbine Blade Leading Edge Cooling With One Row of Normal or Tangential Impinging Jets

Jet impingement cooling has been extensively used in the leading edge region of a gas turbine blade. This study focuses on the effect of jet impinging position on leading edge heat transfer. The test model is composed of a semicylindrical target plate, side exit slots, and an impingement jet plate. A row of cylindrical injection holes is located along the axis (normal jet) or the edge (tangential jet) of the semicylinder, on the jet plate. The jet-to-target-plate distance to jet diameter ratio (z/d) is 5 and the ratio of jet-to-jet spacing to jet diameter (s/d) is 4. The jet Reynolds number is varied from 10,000 to 30,000. Detailed impingement heat transfer coefficient distributions were experimentally measured by using the transient liquid crystal (TLC) technique. To understand the thermal flow physics, numerical simulations were performed using Reynolds-averaged Navier–Stokes (RANS) with two turbulence models: realizable k–ε (RKE) and shear stress transport k–ω model (SST). Comparisons between the experimental and the numerical results are presented. The results indicate that the local Nusselt numbers on the test surface increase with the increasing jet Reynolds number. The tangential jets provide more uniform heat transfer distributions as compared with the normal jets. For the normal jet impingement and the tangential jet impingement, the RKE model provides better prediction than the SST model. The results can be useful for selecting a jet impinging position in order to provide the proper cooling distribution inside a turbine blade leading edge region.

Effects of opening edge treatment and EPS thickness on EPS external thermal insulation composite systems (ETICS) façade reaction‐to‐fire performance based on JIS A1310 standard façade fire test method

AbstractExternal thermal insulation composite systems (ETICS) are quite common in constructions. However, the combustible insulation core induces serious fire disasters, especially considering thermoplastic expanded polystyrene (EPS) has been widely used as insulation core. Most of EPS ETICS building fire is caused by window spreading fire. The window opening edge treatment plays an important role in EPS ETICS fire prevention. Presently, in order to investigate optimal opening edge treatment and EPS thickness effects on EPS ETICS reaction‐to‐fire performance, façade fire tests based on JIS A 1310 standard façade fire test method were carried out by testing a series of EPS ETICS specimens varying EPS thickness, opening edge treatment methods and heating intensity. It is found that back‐wrapping is a good opening edge treatment method. When the EPS ETICS specimen is treated by back‐wrapping opening edge treatment method, the peak temperature, EPS burn area, time (20 minutes) averaged temperature, and heat flux density become low. The time (20 minutes) averaged temperature of each position from T1 to T5 versus EPS thickness is linear at heating intensity 300 or 600 kW. The averaged ratio of EPS burn area above opening (Sa) and below opening (Sb) is approaching 3.058.

A Study on Analytical Methods of FEM-Based Edge Heating System

This paper focuses on analytical methods of a finite-element method (FEM)-based edge heating system. The edge heating system plays a role in maintaining the temperature in the hot rolling process of carbon steel. Carbon steel moves along the production line and maintains the temperature by the edge heating system in the process. Power-of-the-edge heating system is transmitted to carbon steel during the process. Eddy currents are generated in carbon steel by Faraday’s law of electromagnetic induction, and eddy current loss serves as a heat source to increase the temperature. Thus, there is a need for accurate electromagnetic-field analysis and thermal analysis because the eddy current path generated in carbon steel greatly affects the heat distribution in carbon steel. This multiphysics analysis requires high reliability. Accordingly, this paper presents a coupling analysis method using an FEM-based coordinate mapping method as a more accurate analytical method. This paper also established an analytical approach to the edge heating system using the ductility analytical method of this coordinate mapping method.

Synchronized fusion development considering physics, materials and heat transfer

Significant achievements have been made in the last 60 years in the development of fusion energy with the tokamak configuration. Based on the accumulated knowledge, the world is embarking on the construction and operation of ITER (International Thermonuclear Experimental Reactor) with a production of 500 MWf fusion power and the demonstration of physics Q = 10. ITER will demonstrate D–T burn physics for a duration of a few hundred seconds to prepare for the next long-burn or steady state nuclear testing tokamak operating at much higher neutron fluence. With the evolution into a steady state nuclear device, such as the China Fusion Engineering Test Reactor (CFETR), it is necessary to examine the boundary conditions imposed by the combined development of tokamak physics, fusion materials and fusion technology for a reactor. The development of ferritic steel alloys as the structural material suitable for use at high neutron fluence leads to the use of helium as the most likely reactor coolant. This points to the fundamental technology limitation on the removal of chamber wall maximum heat flux at around 1 MW m−2 and an average heat flux of 0.1 MW m−2 for the next test reactor. Future reactor performance will then depend on the control of spatial and temporal edge heat flux peaking in order to increase the average heat flux to the chamber wall. With these severe material and technological limitations, system studies were used to scope out a few robust steady state synchronized fusion reactor (SFR) designs. As an example, a low fusion power design at 131.6 MWf, which can satisfy steady state design requirements, would have a major radius of 5.5 m and minor radius of 1.6 m. Such a design with even more advanced structural materials like Wf/W composite could allow higher performance and provide a net electrical production of 62 MWe. These can be incorporated into the CFETR program.

Topological Heat Transport and Symmetry-Protected Boson Currents

The study of non-equilibrium properties in topological systems is of practical and fundamental importance. Here, we analyze the stationary properties of a two-dimensional bosonic Hofstadter lattice coupled to two thermal baths in the quantum open-system formalism. Novel phenomena appear like chiral edge heat currents that are the out-of-equilibrium counterparts of the zero-temperature edge currents. They support a new concept of dissipative symmetry-protection, where a set of discrete symmetries protects topological heat currents, differing from the symmetry-protection devised in closed systems and zero-temperature. Remarkably, one of these currents flows opposite to the decreasing external temperature gradient. As the starting point, we consider the case of a single external reservoir already showing prominent results like thermal erasure effects and topological thermal currents. Our results are experimentally accessible with platforms like photonics systems and optical lattices.

Stress analysis of functional gradient strip due to transient thermal heat

AbstractThe work is mainly focuses on the analysis of thermal gradients and its effect on thermal stresses in FGM (functional gradient material) grading‐strip made up of TiC‐Ni due to thermal heat with different rate: thermal shock, transient exponential and linear heat. In this paper, asymptotic analytical solution for exponential and linear heat will be investigated. Few models of material grading are considered: (a) models which depend on different volume content of TiC and (b) models with homogeneous layers. Thermal and mechanical properties of the material are assumed different along axis. It is assumed that Poisson's ratio and Young's modulus varies exponentially with the coordinate of the strip. The dependence on different material property idealizations is also investigated. As well for research maximum and minimal thermal stresses in paper compared laminated non‐FGM and FGM strip. The maximum tensile stress obtained for FGM case. At the same time compressive stresses near heated surface for two‐layered strip lager then for three‐layered and less or absent for FGM strip. Heating/cooling opposite edge to thermal shocked ones leads to increase/decrease compressive stress in metal phase part in FGM and layered strip. At the beginning of heat the differences in compressive stress for thermal shock and exponential heat could differ in ten times. Compressive stress in linear heat case increase from beginning and stay stable as maximum from three heat cases as long as edge heat up to maximum temperature. The results obtained in this research paper allow us to analyze the validity of this method and to understand principles of thermal behavior on FGM‐strip in a case of different conditions and different heat transfer rate.

Influence of Local Heating on Marangoni Flows and Evaporation Kinetics of Pure Water Drops.

The effect of localized heating on the evaporation of pure sessile water drops was probed experimentally by a combination of infrared thermography and optical imaging. In particular, we studied the effect of three different heating powers and two different locations, directly below the center and edge of the drop. In all cases, four distinct stages were identified according to the emerging thermal patterns. In particular, depending on heating location, recirculating vortices emerge that either remain pinned or move azimuthally within the drop. Eventually, these vortices oscillate in different modes depending on heating location. Infrared data allowed extraction of temperature distribution on each drop surface. In turn, the flow velocity in each case was calculated and was found to be higher for edge heating, due to the one-directional nature of the heating. Additionally, calculation of the dimensionless Marangoni and Rayleigh numbers yielded the prevalence of Marangoni convection. Heating the water drops also affected the evaporation kinetics by promoting the "stick-slip" regime. Moreover, both the total number of depinning events and the pinning strength were found to be highly dependent on heating location. Lastly, we report a higher than predicted relationship between evaporation rate and heating temperature, due to the added influence of the recirculating flows on temperature distribution and hence evaporation flux.

Radio frequency heating of corn flour: Heating rate and uniformity

Abstract Non-uniform heating is a major challenge for using radio frequency (RF) heat treatment in pasteurization of low moisture food products. The objective of this study was to evaluate the effect of different electrode gaps, moisture content (MC), bulk density and surrounding materials on RF heating uniformity and rate in corn flour. Additionally, the dielectric and thermal properties of corn flour were determined as affected by MC, temperature (°C), and frequency (MHz). Changes in MC, water activity (a w ) and color in the sample after RF heating were measured to evaluate treatment effect on food quality. A precision LCR meter and a liquid test fixture were used to study DP of the sample at RF frequency ranging from 1 to 30 MHz. The RF heating uniformity and temperature profiles of corn flour as exposed to RF heating were obtained with an infrared camera and a data logger connected to a fiber optic sensor. The DP values increased with increasing MC and temperature, but decreased with frequency. The heating rate increased from 3.5 to 6.8 °C min − 1 with increasing MC (from 10.4 to 16.7%), but decreased from 12.7 to 5.2 °C min − 1 with increasing electron gap (from 11 to 15 cm). The corner and edge heating were observed at all layers of the samples for all the distances, and the hottest and the most uniform layer were determined as the middle layer at an electrode gap of 15 cm. Glass petri dish provided better uniformity than those of polyester plastic petri dish. Covering by foam led to more uniform RF heating uniformity in corn flour, and better moisture and a w distribution. This study provided useful information to develop an effective RF process as an alternative of conventional thermal treatments for pasteurization of low-moisture products. Industrial relevance This paper describes a novel methodology based on Radio Frequency heating to pasteurize food powder while maintaining the quality. The study addresses the ever-increasing global demand from consumers for safe food products.

B2.5-Eirene modeling of radial transport in the MAGPIE linear plasma device

Radial transport in helicon heated hydrogen plasmas in the MAGnetized Plasma Interaction Experiment (MAGPIE) is studied with the B2.5-Eirene (SOLPS5.0) code. Radial distributions of plasma density, temperature and ambipolar potential are computed for several magnetic field configurations and compared to double Langmuir probe measurements. Evidence for an unmagnetized ion population is seen in the requirement for a convective pinch term in the continuity equation in order to fit the centrally peaked density profile data. The measured slightly hollow electron temperature profiles are reproduced with combinations of on-axis and edge heating which can be interpreted as helicon and Trivelpiece–Gould wave absorption, respectively. Pressure gradient driven radial charged particle diffusion is chosen to describe the diffusive particle flux since the hollowness of the temperature profiles assists the establishment of on-axis density peaking.

Inter-ELM heat loads on tungsten leading edge in the KSTAR divertor

A series of leading edge heat load experiments are performed in KSTAR to study power balance and to support a divertor shaping decision on ITER. Tungsten blocks with leading edges of various heights were fabricated, adjusted and mounted to central divertor of KSTAR with extreme care to avoid the intrinsic misalignment caused by engineering limits. The results from IR measurements and COMSOL simulation are consistent with each other and the power discrepancy found at JET does not exist at KSTAR. A simple calculation with geometrical projection can be used to foreseen the heat load on divertor blocks with arbitrary shapes. Therefore, the results present in this paper are valuable for new design of divertor blocks.

Cross-Flow Heat Exchanger: Volume-Averaging Formulation of a Unit Cell Model and Thermal Performance Analysis

A formulation of the unit cell model and the corresponding thermal performance analysis for the cross-flow heat exchanger are carried out, with the design goal of dissipating 175 W from a high-power electronic chip in a compact space. A liquid to liquid heat exchanger in the cross-flow arrangement is preferred due to its compact size and high effectiveness. The unit cell model is formulated based on the volume-averaging method to determine the heat transfer coefficient involving two heat exchanging fluids and a solid. The various factors such as channel shape, channel edge length, channel size, and heat exchanger material can be examined based on the unit cell model. The obtained heat transfer coefficients are used for the estimation of the heat exchanger thermal performance based on the effectiveness–number of transfer units (NTU) correlation. To verify the model formulation, the heat and fluid flow over the cross-flow heat exchangers are investigated through the full-field numerical computation. The amount of heat exchanged from the numerical computation is extracted and compared with the predicted results from the unit cell model. A fairly good agreement is obtained between the two approaches. Based on the unit cell model, an aluminum cross heat exchanger with eight channel layers for the hot and cold fluids, 15 channels in each layer with a channel diameter of 2 mm, is able to meet the design target.

Allowable heat load on the edge of the ITER first wall panel beryllium flat tiles

Plasma facing components are usually qualified to a given heat load density applied at the top face of the armour tiles with normal incidence angle. When employed in tokamak fusion machines, heat loading on the tile sides is possible due to optimised shaping, that doesn't provide edge shadowing for all design situations. An edge heat load may occur both at the tile and component scales. The edge load needs to be controlled and quantified. The adequate control of edge heat loads is especially critical for water cooled components that uses armour tiles which are bonded to the heat sink, for ensuring the long-term integrity of the tile bonding. An edge heat load allowance criterion of 10% of the top heat load is proposed. The 10% criterion is supported by experimental heat flux tests.

Modeling radio frequency heating of food moving on a conveyor belt

A multiphysics model that coupled electric fields and heat transfer was developed to simulate the radio frequency (RF) heating of food moving on a conveyor belt. A discrete moving step approach was used in the simulation. The total power absorption increased considerably during the entry of the sample into the RF system, remained stable when the sample was fully covered by the top and bottom electrodes, and decreased when the sample moved out of the system. Edge and corner heating was observed from the power absorption distribution and electric field distribution. The model was validated by heating a rectangular container of wheat kernels moving on a conveyor belt in a RF system (27.12MHz, 6kW). The predicted spatial temperatures in top, middle, and bottom layers showed less than 3.5°C lower prediction than the experimental result. The measured anode current showed a good linear correlation with the predicted total power absorption. The optimum number of discrete moving steps was determined to be nine for accurate temperature prediction with total conveyor belt movement distance of 1.13m which is equivalent to optimize step size of 0.1256m/step (0.3m for entry and exit, respectively, and 0.53m for fully covered by electrodes) at speed of 14.23mh−1. The movement of food product could help improve the heating uniformity of RF heating process.

Frequency Distribution in Domestic Microwave Ovens and Its Influence on Heating Pattern.

In this study, snapshots of operating frequency profiles of domestic microwave ovens were collected to reveal the extent of microwave frequency variations under different operation conditions. A computer simulation model was developed based on the finite difference time domain method to analyze the influence of the shifting frequency on heating patterns of foods in a microwave oven. The results showed that the operating frequencies of empty and loaded domestic microwave ovens varied widely even among ovens of the same model purchased on the same date. Each microwave oven had its unique characteristic operating frequencies, which were also affected by the location and shape of the load. The simulated heating patterns of a gellan gel model food when heated on a rotary plate agreed well with the experimental results, which supported the reliability of the developed simulation model. Simulation indicated that the heating patterns of a stationary model food load changed with the varying operating frequency. However, the heating pattern of a rotary model food load was not sensitive to microwave frequencies due to the severe edge heating overshadowing the effects of the frequency variations.